Conventionally a fan rotor for compressing air comprises a disc having a plurality of radially extending blades mounted thereon. The fan blades are mounted on the disc by inserting the inner end of the blade in a correspondingly shaped retention groove in the outer face of the disc periphery. Separate wall members bridge the space between pairs of adjacent blades to define the inner wall of an annular gas passage in which the fan rotor is operationally located.
It is known to provide a seal between the wall members and the adjacent fan blades by providing resilient strips bonded to the wall member edges adjacent the fan blades. The strips protrude so that they abut and seal the adjacent fan blades. This prevents air leaking past the inner wall of the annulus.
However the above described arrangement has the main drawback that the resilient strips are necessarily in a close fit with the adjacent blades, leading to assembly difficulties
WO 93/22539 discloses an improvement to the above arrangement where the inner wall of the flow annulus is defined by a plurality of wall members which are provided with resilient strips allowing for easier assembly.
The wall members bridge the space between adjacent fan blades and each comprise a platform having a foot which engages within a similarly shaped groove of the disc. Flanges are bonded to the platform, each flange having a resilient seal. As the fan rotates the flanges are directed outwards into sealing contact with the adjacent fan blades to seal the inner wall of the flow annulus.
This arrangement, however, has certain disadvantages. Aerodynamic losses occur due to the necessary gap between the blade surface and seal. The gap in the prior art arrangement is required to be relatively large to accommodate blade dynamic movement during for example bird impact and when a blade may become detached. The flange sealing element normally operates (provides a seal) at around 6000*G. However, as the rotor speed increases, the end of the flange is subject to increased load and the seal becomes more prone to `flip out` leading to efficiency losses and vibration problems. In addition the rubber seals tend to split and degrade during use and need to be replaced at regular intervals. Another problem is that the seals pick up titanium oxides from the blade surface causing damage to the blade surface through scratching. The seals are also costly to produce and are undesirably heavy.